Microreplication is a process where softened polymer film or an extruded material is brought into contact with a pressure nip such that an extrudate or softened film is pressed against a tool with fine patterning or a particular surface topography on it. The pattern or topography is reversely transferred onto the side of the material in contact with the tool. The foregoing process is widely used in roll to roll manufacturing methods to produce patterned or replicated products such as reflective materials, and other optical films.
A typical microreplication process includes a heating means to soften the polymer material which may be provided as a film or extrudate, and then using heat and pressure to impress the pattern onto the polymer material, and then cooling the material to cool the patterned polymer before being rolled up, sheeted or otherwise collected.
The manufacturing speed can be limited by the slowest process, which can be determined by any one of the steps (heating, pressing, cooling) mentioned above. With advancement in heating, such as through NIR, the cooling step then may become the bottle neck, i.e. the film does not get cooled fast enough so the production speed has to be lowered to provide sufficient time for the film to cool further. Currently, the cooling is conducted through the employment of cooling air, such as recirculating fans, blowers, chilled rollers, and the like.
There are a number of prior methods to improve cooling of films or webs. One such example is to use heat conduction to remove heat from the film. It is well known that heat transfer coefficient of heat conduction is the order of magnitude higher than that of heat convection (by air). Cooling by conduction is commonly achieved by means of a continuous cooling belt, single or double. This type of equipment found broad implementation in pharmaceutical and food industries. Typically, such a thin metal belt (stainless steel or brass) is connected at its ends to form a closed loop. The belt is kept cooled by spraying chilled water or other cooling agent on the side of the belt opposite to the surface that requires cooling. Due to high heat transfer through the metal, heat is efficiently removed from the hot surface. In this process, it is critical to ensure a good contact between the hot and cold surfaces. In the event that there is an air gap between the surfaces of the cooling belt and the film being cooled, the heat transfer coefficient drops dramatically and cooling becomes inefficient. Exemplary manufacturers of such cooling equipment include Sandvik and BBA.
Therefore, there is a need for an improvement for the cooling step in order to facilitate the production of the patterned product having a particular surface topography.